1. Field of the Invention
The present invention relates to a cylindrical fluid-filled elastic mount, and more particularly to an improved structure of a cylindrical fluid-filled elastic mount which has a plurality of fluid chambers filled with a non-compressible fluid so as to exhibit an excellent damping effect on the basis of flow of the fluid therebetween.
2. Discussion of Related Art
As a damping connecting device of a type adapted to be interposed between two members of a vibration-transmitting system so as to elastically connect these members, there is known a cylindrical fluid-filled elastic mount in which a center shaft member to be attached to the one of the members to be elastically connected and an outer cylindrical member to be attached to the other member of the two members disposed outside in a direction perpendicular to the axial direction with a suitable distance around the center shaft, and are elastically connected to each other by an elastic body interposed therebetween. A plurality of fluid chambers filled with a non-compressible fluid is formed in the elastic body so as to be located in the axial direction or in the circumferential direction. Further, an orifice passage is formed which permits predetermined two fluid chambers of the plurality of fluid chambers to communicate each other, thereby, upon application of vibration, the fluid filled in each of the two fluid chambers is allowed to flow mutually through the orifice passage.
In the cylindrical fluid-filled elastic mount described above, which is capable of exhibiting damping effect upon an application of vibrations, on the basis of flows (such as resonance) of a fluid through the orifice passage. The thus constructed cylindrical fluid-filled elastic mount has been suitably used as an engine mount, a body mount, or a suspension bush such as a strut bar cushion for a motor vehicle, for instance.
In the cylindrical fluid-filled elastic mount described above, the applied vibration to be controlled is in a frequency region corresponding to the cross-sectional area and the length of the passage of the orifice passage (hereinafter may be referred to as “flow path”). Therefore, an orifice member cooperating with the outer cylindrical member to form the orifice passage therebetween is disposed in a pocket of elastic body which provides the fluid chamber. Whereby, a higher degree of freedom in designing the length and the cross-sectional area of fluid flow is realized, and the tuning range of frequency is easily and suitably tuned. Such a cylindrical fluid-filled elastic mount is disclosed in, JP-A-63-210431, JP-2583212, and JP-U-B-6-25731, for instance.
Such a conventional cylindrical fluid-filled elastic mount, includes; a center shaft member; a metal sleeve disposed radially outwardly of the center shaft member with a predetermined radial distance therebetween provided with a plurality of windows; an elastic body interposed between the center shaft member; a metal sleeve for elastic connection therebetween; a plurality of pockets provided in the elastic body and being open in an outer circumferential surface of the metal sleeve through the corresponding windows thereof; a communication groove provided so that two pockets to be connected, of the plurality of pockets, communicate therebetween in a circumferential direction so as to be open in the outer circumferential surface; an orifice member provided with an orifice groove at an outer surface thereof, which has the opposed end portions provided at an end of the orifice groove is inserted in the communication groove so as to be fixed to the communication groove; and an outer cylindrical member fitted on the metal sleeve to close the plurality of windows and the orifice groove, whereby the plurality of fluid chambers filled with a non-compressible fluid are defined by the corresponding pockets, at the same time an orifice passage is defined by the corresponding orifice groove.
However, in the conventional cylindrical fluid-filled elastic mount described above, since a relatively hard material having a high rigidity such as a metal or a resin is used as the material for the orifice member, it is cumbersome to seal the orifice passage formed by the orifice member, which involves a problem that the damping effect may not be exhibited sufficiently in the case that the fluid leaks from the orifice passage. In addition, if the orifice member formed of metal or resin abuts or touches other apparatus forming members when vibrations are applied, there arises a problem of generating noise and the like problems.
To avoid the drawback described above, it may be considered to form the orifice member by an elastic material, especially, a vulcanized product of elastic material. At the same time, at least both-side walls of a trough-form protrusion provided in an orifice groove end portion as an orifice member are made of rubber, and the trough-form protrusion is inserted in a communication groove formed in a communication groove-forming elastic member disposed on the outer peripheral portion of the metal sleeve. When this structure is employed, the problems described below may occur.
The outer cylindrical member is subjected to diameter-reducing operation by drawing to fix the outer cylindrical member on the metal sleeve. Due to such diameter-reducing operation, compressive action is applied to the both-side elastic portions forming the communication groove. Accordingly, the rubber falls into the communication groove from both sides, or expands as seen in FIG. 14. Thereby, the both-side walls of the trough-form protrusion of the orifice member inserted in the communication groove are deformed and fall to the orifice groove side, as a result, the cross-sectional area of the orifice passage has a smaller amount of flow of fluid. Therefore, there arises a problem that it is difficult to sufficiently achieve the intended damping characteristic based on the flow of fluid in the orifice passage. Also, there arises a problem that the deformation of both-side walls made of rubber may deteriorate sealing.